<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>3-4 Vue.set</title>
</head>
<body>
<div id="app">
  <div>{{a}}</div>
  <div>{{obj.b}}</div>
</div>
</body>
<script src="./js/vue.js"></script>
<script>
  var vm=new Vue({
    el:"#app",
    data:{
      a:"I am attribute a of root response ",
      obj:{}
    }
  })
  Vue.set(vm.obj,'b',"I am attribute obj.b of appended response")
</script>
</html>